Matroids are an abstraction of several combinatorial objects, among them graphs and matrices. The word matroid was coined by Whitney in 1935 in his landmark paper "On the abstract properties of linear dependence." In defining a matroid Whitney tried to capture the fundamental properties of dependence that are common to graphs and matrices. Matroid theory provides a framework in which problems in combinatorial optimization, operations research and graph theory become simpler to understand. With links to books, a bibliography of matroid papers, software, and home pages of people in matroid theory.